Sort of light in swamp (5)
I believe the answer is:
flood
This clue is a double definition.
'sort of light' is the first definition.
(I know that flood is a type of light)
'swamp' is the second definition.
(I know that swamp can be written as flood)
'in' is the link.
(Other definitions for flood that I've seen before include "Spate" , "Overflow of water" , "Brim over" , "Inundate" , "Overwhelming amount" .)